KR20090066232A - Liquid crystal display - Google Patents

Abstract

A liquid crystal display device having a liquid crystal layer held between a pair of substrates includes a scan line extending in a row direction of a pixel, a signal line extending in a column direction of a pixel, a pixel electrode disposed in each pixel and having slits, and a pixel electrode. And a first common electrode facing each other via an interlayer insulating film, and a second common electrode extending parallel to the slit in the same layer as the pixel electrode and disposed adjacent to the pixel electrode.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

This application is based on the JP Patent application 2007-326192 of an application on December 18, 2007, The content is taken in here as a reference.

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a structure in which a pixel electrode and a common electrode are provided on one substrate constituting the liquid crystal display panel.

In recent years, flat panel display devices have been actively developed, and among them, liquid crystal display devices have attracted particular attention from advantages such as light weight, thinness, and low power consumption. In particular, in an active matrix liquid crystal display device in which switching elements are assembled in each pixel, a structure using a lateral electric field (including a fringe electric field) such as an In-Plane Switching (IPS) mode or a Fringe Field Switching (FFS) mode is noted. (See, for example, Japanese Patent Laid-Open No. 2005-107535 and Japanese Patent Laid-Open No. 2006-139295).

The liquid crystal display device in the IPS mode or the FFS mode includes a pixel electrode and a common electrode arranged on the array substrate, and switches the liquid crystal molecules in a transverse electric field substantially parallel to the main surface of the array substrate. Moreover, the polarizing plates arrange | positioned so that a polarization axis may orthogonally cross mutually are arrange | positioned at each outer surface of an array substrate and an opposing board | substrate. Such arrangement of the polarizing plate realizes display of a black screen, for example, when no voltage is applied, and gradually increases transmittance (modulation rate) by applying a voltage corresponding to a video signal to the pixel electrode to realize display of a white screen. . In such a liquid crystal display device, since the liquid crystal molecules rotate in a plane substantially parallel to the main surface of the substrate, the polarization state does not greatly affect the incidence direction of the transmitted light, so that the viewing angle dependency is small and has a wide viewing angle characteristic. There is a characteristic.

In particular, in the liquid crystal display device of the FFS mode, the pixel electrode is disposed to face the common electrode via the interlayer insulating film. This pixel electrode has slits facing the common electrode. The liquid crystal molecules are driven by an electric field formed between the pixel electrode and the common electrode through such slits.

In the pixel electrode of such a shape, an electric field does not generate | occur | produce in the area | region where the slit is not formed, especially the peripheral edge of a pixel electrode. In the region where such an electric field does not occur, the liquid crystal molecules are not driven (that is, the orientation of the liquid crystal molecules does not change from the rubbing direction). For this reason, at the time of voltage application, the modulation rate of the light which permeate | transmits a liquid crystal layer does not change. Therefore, the improvement of the transmittance | permeability of the liquid crystal display panel, ie, the improvement of the aperture ratio of each pixel is desired.

An object of the present invention is to provide a liquid crystal display device capable of improving transmittance and displaying a good image of display quality.

According to an aspect of the invention,

A liquid crystal display device having a structure in which a liquid crystal layer is held between a pair of substrates,

A scanning line extending in the row direction of the pixel,

A signal line extending in the column direction of the pixel,

A pixel electrode disposed for each pixel and having a slit;

A first common electrode facing the pixel electrode via an interlayer insulating film;

A second common electrode extending in parallel with the slit and disposed adjacent to the pixel electrode in the same layer as the pixel electrode;

There is provided a liquid crystal display device comprising:

According to the present invention, it is possible to provide a liquid crystal display device capable of improving transmittance and displaying a good image of display quality.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be understood by practice of the invention. The objects and advantages of the present invention will be realized and attained, in particular, by the means and combinations thereof disclosed below.

The accompanying drawings, which are incorporated in and constitute a part of this specification, describe embodiments of the invention and, together with the foregoing summary and detailed description, serve to explain the principles of the invention.

EMBODIMENT OF THE INVENTION Hereinafter, the liquid crystal display device which concerns on one Embodiment of this invention is demonstrated with reference to drawings. Here, a liquid crystal mode in which a liquid crystal display is provided with a pixel electrode and a common electrode on one substrate and mainly switches liquid crystal molecules using a transverse electric field (or a horizontal electric field substantially parallel to the substrate) formed therebetween. The device will be described as an example.

As shown in FIG. 1, FIG. 2, and FIG. 3, a liquid crystal display device is a liquid crystal display device of an active matrix type, and is equipped with liquid crystal display panel LPN. The liquid crystal display panel LPN includes an array substrate AR, an opposing substrate CT disposed to face the array substrate AR, and a liquid crystal layer LQ held between the array substrate AR and the opposing substrate CT. Such a liquid crystal display device is provided with the display area DSP which displays an image. This display area DSP is comprised by several pixel PX arrange | positioned in m * n matrix form.

Array substrate AR is formed using the insulating substrate 20 which has light transmittance, such as a glass plate and a quartz plate. As shown in Fig. 1 and Fig. 2, this array substrate AR has m x n pixel electrodes EP arranged for each pixel PX and n scanning lines Y (each extending in the row direction H of each pixel PX) in the display area DSP. Y1 to Yn, m signal lines X (X1 to Xm) each extending in the column direction V of each pixel PX, and m x n switching elements arranged in an area including an intersection of the scan line Y and the signal line X in each pixel PX. W, the first common electrode COM1 and the like arranged to face each other via the pixel electrode EP and the interlayer insulating film IL are provided.

The array substrate AR is also at least part of the scan line driver YD connected to the n scan lines Y or at least part of the signal line driver XD connected to the m signal lines X in the driving circuit region DCT around the display area DSP. Etc. are provided. The scanning line driver YD sequentially supplies the scanning signals (drive signals) to the n scanning lines Y based on the control by the controller CNT. Further, the signal line driver XD supplies a video signal (driving signal) to the m signal lines X at timings at which the switching elements W in each row are turned on by the scanning signal based on the control by the controller CNT. Thereby, the pixel electrode EP of each row is set to the pixel potential corresponding to the video signal supplied through the corresponding switching element W, respectively.

Each switching element W is comprised by thin film transistors, for example. The semiconductor layer of the switching element W can be formed by polysilicon, amorphous silicon, etc., for example. The gate electrode WG of the switching element W is connected to the scanning line Y (or the gate electrode WG is formed integrally with the scanning line Y). The source electrode WS of the switching element W is connected to the signal line X (or the source electrode WS is formed integrally with the signal line X), and is contacting the source region of the semiconductor layer. The drain electrode WD of the switching element W is connected to the pixel electrode EP and is in contact with the drain region of the semiconductor layer.

The 1st common electrode COM1 is arrange | positioned, for example in each pixel PX, and is electrically connected to the common wiring C to which the common potential is supplied. This first common electrode COM1 is covered by the interlayer insulation film IL. The pixel electrode EP is disposed to face the first common electrode COM1 on the interlayer insulating film IL.

2 and 3, the pixel electrode EP has a plurality of slits SL facing the first common electrode COM1. The pixel electrode EP and the first common electrode COM1 are formed of a conductive material having light transmittance, such as indium tin oxide (ITO), indium zinc oxide (IZO), or the like. The surface in contact with the liquid crystal layer LQ of the array substrate AR is covered with the alignment film 36a.

On the other hand, the opposing board | substrate CT is formed using the insulated substrate 30 which has light transmittance, such as a glass plate and a quartz plate. In particular, in the color display type liquid crystal display device, as shown in FIG. 2, the counter substrate CT has a black matrix 32 partitioning each pixel PX on the inner surface of the insulating substrate 30, that is, the surface facing the liquid crystal layer LQ. ), And a color filter layer 34 disposed in each pixel PX surrounded by the black matrix 32. The counter substrate CT may further include a shield electrode for mitigating the influence of an external electric field, an overcoat layer disposed at a relatively thick film thickness, and the like to planarize the unevenness of the surface of the color filter layer 34. .

The black matrix 32 is disposed on the insulating substrate 30 so as to face wiring portions such as scan lines Y, signal lines X, and switching elements W provided in the array substrate AR. The color filter layer 34 is disposed on the insulating substrate 30 and is formed of colored resins each colored in three primary colors such as a plurality of different colors, for example, red, blue, and green. Red coloring resin, blue coloring resin, and green coloring resin are arrange | positioned corresponding to a red pixel, a blue pixel, and a green pixel, respectively. The surface which contacts the liquid crystal layer LQ of the opposing board | substrate CT is covered by the orientation film 36b.

When such an opposing substrate CT and the array substrate AR as described above are arranged so that each of the alignment film 36a and the alignment film 36b face each other, a predetermined gap is formed by spacers (not shown) disposed between them. Liquid crystal layer LQ is comprised by the liquid crystal composition containing liquid crystal molecule LM enclosed in the gap formed between the alignment film 36a of these array substrate AR, and the alignment film 36b of the opposing board | substrate CT. The liquid crystal molecules LM contained in the liquid crystal layer LQ are aligned by the regulating force by the alignment film 36a and the alignment film 36b. That is, when the potential difference is not formed between the pixel electrode EP and the first common electrode COM1 (that is, no electric field is formed between the pixel electrode EP and the first common electrode COM1), the liquid crystal molecule LM The long axis D1 is oriented so as to face an orientation parallel to the rubbing direction S of the alignment film 36a and the alignment film 36b.

In addition, the liquid crystal display device includes an optical element OD1 provided on one outer surface of the liquid crystal display panel LPN (that is, the surface opposite to the surface in contact with the liquid crystal layer LQ of the array substrate AR), and the other of the liquid crystal display panel LPN. Optical element OD2 provided in the outer surface (namely, the surface opposite to the surface which contacts liquid crystal layer LQ of opposing board | substrate CT) is provided. These optical elements OD1 and OD2 comprise polarizing plates, for example, and realize the normally black mode in which the transmittance of liquid crystal display panel LPN becomes the lowest (that is, displays a black screen) in the case of an electroless field.

The liquid crystal display device also has a backlight unit BL arranged on the array substrate AR side with respect to the liquid crystal display panel LPN.

In such a liquid crystal display, as shown in FIG. 3, when a potential difference is formed between the pixel electrode EP and the first common electrode COM1 (that is, a voltage to which a voltage of a potential different from the common potential is applied to the pixel electrode EP). In the application), an electric field E is formed between the pixel electrode EP and the first common electrode COM1. At this time, the liquid crystal molecule LM is driven such that its long axis D1 is oriented in a direction parallel to the electric field E from the rubbing direction S. FIG. Thus, when the orientation of the long axis D1 of the liquid crystal molecule LM changes from the rubbing direction S, the modulation rate with respect to the light which permeate | transmits the liquid crystal layer LQ changes. For this reason, a part of backlight light which permeate | transmitted liquid crystal display panel LPN from backlight unit BL permeate | transmits 2nd optical element OD2, and displays a white screen. That is, the transmittance of the liquid crystal display panel LPN changes depending on the magnitude of the electric field E. In the liquid crystal mode using the transverse electric field, the backlight is selectively transmitted in this manner to display an image.

In particular, in the present embodiment, the liquid crystal display device has a second common electrode COM2 disposed in the display area DSP. The second common electrode COM2 extends in the direction parallel to the major axis L or the signal line X of the slit SL of the pixel electrode EP. In the example shown in FIG. 4A, the major axis L of the slit SL is formed in parallel with the column direction V. FIG. The slit SL is formed in a rectangular shape, for example. The long side d of the slit SL is parallel to the major axis L. The plurality of slits SL are arranged in the row direction H. FIG. That is, in the example shown in FIG. 4A, the second common electrode COM2 is disposed extending in a direction parallel to the major axis L of the slit SL, that is, in the column direction V. As shown in FIG.

The second common electrode COM2 is disposed adjacent to the pixel electrode EP on the same layer as the pixel electrode EP. These pixel electrodes EP and the second common electrode COM2 are spaced apart, and the side edges of the pixel electrodes EP2 face each other. A gap extending in the column direction V is formed between the pixel electrode EP and the second common electrode COM2 similarly to the slit SL. That is, these pixel electrodes EP and the second common electrode COM2 are electrically insulated. The first common electrode COM1 and the second common electrode COM2 are electrically connected through a contact hole (not shown). That is, the first common electrode COM1 and the second common electrode COM2 have the same potential, and both are electrically connected to the common wiring C.

As shown in FIG. 4B, in the array substrate AR, the first common electrode COM1 is disposed on the insulating substrate 20. The first common electrode COM1 and the insulating substrate 20 are covered with the first insulating film ILa of the interlayer insulating film IL. The signal line X is disposed on the first insulating film ILa. The signal line X and the first insulating film ILa are covered by the second insulating film ILb of the interlayer insulating film IL. The second common electrode COM2 is disposed on the second insulating film ILb together with the pixel electrode EP.

Since the first common electrode COM1 and the second common electrode COM2 are electrically connected, when the potential difference is formed between the pixel electrode EP and the first common electrode COM1 and the second common electrode COM2, the pixel electrode EP and the first common electrode are formed. Between the electrodes COM1, the electric field E is formed in the direction orthogonal to the long side d, ie, the row direction H, through the slit SL. At the time of voltage application, in the region where the slit SL is formed, the liquid crystal molecules LM are oriented in the direction parallel to the electric field E from the rubbing direction S. Here, in the main plane of the array substrate AR, the rubbing direction S is set in the direction crossing the column direction V. As shown in FIG.

In addition, at the time of voltage application, the electric field E is formed also in the periphery of the pixel electrode EP similarly to the area | region in which the slit SL is formed. That is, as shown in Fig. 4C, between the second common electrode COM2 and the pixel electrode EP in the region where the slit SL is not formed, especially in the side edge in the column direction V of the pixel electrode EP, that is, in the vicinity of the signal line X. An electric field E is formed in the gap.

In this gap, the electric field E is formed in the direction orthogonal to the side edge which opposes the 2nd common electrode COM2 of the pixel electrode EP, ie, the row direction H. As shown in FIG. For this reason, even when the voltage is applied, even in the peripheral edge of the pixel electrode EP, the liquid crystal molecules LM are oriented in the direction parallel to the electric field E from the rubbing direction S. The electric field E formed in the area | region around this pixel electrode EP is parallel to the electric field E of the area | region in which the slit SL was formed.

Therefore, in the present embodiment, the peripheral edge of the pixel electrode EP, in particular, the area along the signal line can be made effective, so that the transmittance of the liquid crystal display panel LPN at the time of voltage application can be improved.

The second common electrode COM2 extends in parallel with the slit SL having a long axis L parallel to the column direction V, and may be disposed to face the signal line X, and may be disposed between the signal line X and the pixel electrode EP (that is, of the signal line X). It may be arranged so as not to overlap directly above. 4A and 4B, the second common electrode COM2 is disposed to face the signal line X via the second insulating film ILb. In this case, the invalid area between the pixels can be reduced. In other words, the distance between adjacent pixel electrodes EP can be shortened with the signal line X therebetween. Therefore, high definition can be achieved.

In addition, when the signal line X is disposed between the insulating substrate 20 and the first insulating film ILa, and the second common electrode COM2 is disposed on the second insulating film ILb, the second common electrode COM2 and the signal line X are formed. The first insulating film ILa and the second insulating film ILb are interposed. That is, at least one insulating film may be interposed between the second common electrode COM2 and the signal line X.

The second common electrode COM2 is formed of the same material as the pixel electrode EP. That is, after forming a conductive material having light transmittance such as ITO or IZO on the interlayer insulating film IL, the second common electrode COM2 is patterned at the same time as the pixel electrode EP is patterned. Thereby, the pixel electrode EP and the 2nd common electrode COM2 can be formed by the same process. Thereby, since it is not necessary to add a new manufacturing process which patterns the 2nd common electrode COM2, manufacturing cost can be suppressed. In addition, another manufacturing process may be added, and the second common electrode COM2 may be formed by a process different from the pixel electrode EP. In this case, the second common electrode COM2 may be formed of a material different from that of the pixel electrode EP.

The effect by the structure of this embodiment is demonstrated compared with a comparative example.

In the comparative example shown in FIG. 5A, the pixel electrode EP has a plurality of slits SL formed to be inclined in two directions with respect to the row direction H. As shown in FIG. That is, the slit SL is formed so that the long axis L may incline with respect to the row direction H. As shown in FIG. The slit SL is formed in parallelogram shape, for example. The long side d of the slit SL is parallel to the major axis L. In addition, the plurality of slits SL are arranged in the column direction V orthogonal to the row direction H. FIG. Here, the rubbing direction S is the same direction as the row direction H in the main plane of the array substrate AR.

When the potential difference is formed between the pixel electrode EP and the first common electrode COM1, the electric field E is formed in the direction orthogonal to the long side d through the slit SL. By this electric field E, the liquid crystal molecule LM is driven and orientated in a direction parallel to the electric field E from the rubbing direction S. That is, at the time of voltage application, in the region where the slit SL is formed, the liquid crystal molecules LM are oriented in the direction parallel to the electric field E from the rubbing direction S.

On the other hand, in the region where the slit SL is not formed, particularly the peripheral edge of the pixel electrode EP, even if a potential difference is formed between the pixel electrode EP and the first common electrode COM1, the electric field E is not formed. As shown in FIG. 5B, for example, the electric field E is not formed in the region D near the signal line X of the pixel electrode EP. In such a region D, since the orientation of the liquid crystal molecules LM does not change from the rubbing direction S, the modulation rate for light passing through the liquid crystal layer LQ does not change. In other words, the area D becomes an invalid area.

In contrast, the liquid crystal display device of the present embodiment includes a second common electrode COM2 extending in a direction parallel to the major axis L of the slit SL of the pixel electrode EP and disposed adjacent to the pixel electrode EP. Such a second common electrode COM2 is electrically connected to the first common electrode COM1 facing the pixel electrode EP via the interlayer insulating film IL.

For this reason, when the potential difference is formed between the pixel electrode EP and the first common electrode COM1, an electric field E is formed between the pixel electrode EP and the second common electrode COM2 even in the peripheral edge of the pixel electrode EP in which no slit SL is formed. . The electric field E formed in the region where such a slit is not formed is parallel to the electric field formed between the pixel electrode EP and the first common electrode COM1 via the slit SL. For this reason, at the time of voltage application, the orientation direction of the liquid crystal molecules LM at the periphery of the pixel electrode EP coincides with the orientation direction of the liquid crystal molecules LM in the region where the slit SL is formed.

In this way, the peripheral edge of the pixel electrode EP can be made effective, and the width of the invalid region D can be made smaller than that of the comparative example. Thereby, it becomes possible to improve the aperture ratio and transmittance of the liquid crystal display panel LPN.

In addition, in the comparative example shown in Fig. 5A, the transmittance when the same voltage is applied in the present embodiment shown in Figs. 4A and 4B with respect to the transmittance when the maximum voltage is applied (that is, when displaying a white screen). Became 1.2 times and the improvement of the transmittance | permeability was confirmed.

Next, the modification of this embodiment is demonstrated.

In this modification, the liquid crystal display device is equipped with the 2nd common electrode COM2 similarly to this embodiment. As shown in FIG. 6A, the slit SL of the pixel electrode EP is formed such that its major axis L is parallel to the column direction V. FIG. The second common electrode COM2 extends in parallel with the major axis L of the slit SL. As shown in FIG. 6B, the second common electrode COM2 is formed on the same layer as the pixel electrode EP as in the above-described embodiment. The second common electrode COM2 is disposed to face the signal line X via the second insulating film ILb.

In addition, in the modification, as shown to FIG. 6A and 6B, the 2nd common electrode COM2 has some opening SP. That is, the opening portion SP is formed to face the signal line X.

In the opening SP, no capacitor is formed between the signal line X and the second common electrode COM2. That is, by forming the opening SP, the capacitance generated between the signal line X and the second common electrode COM2 is reduced. For this reason, it becomes possible to suppress the increase of the power consumption of a liquid crystal display device. Therefore, in this modification, it becomes possible to improve the aperture ratio and transmittance of the liquid crystal display panel LPN at the time of voltage application, and also to reduce the power consumption of the liquid crystal display device.

As explained above, according to the liquid crystal display device of this embodiment, a transmittance | permeability can be improved and it becomes possible to display the favorable image of a display quality.

In addition, this invention is not limited to the said embodiment, In the implementation stage, a component can be modified and actualized in the range which does not deviate from the summary. In addition, various inventions can be formed by appropriate combination of a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components disclosed in the embodiment. Moreover, you may combine suitably the component over different embodiment.

For example, in the above-described embodiment, the pixel electrode EP has a slit SL parallel to the signal line X, and the second common electrode COM2 parallel to the slit SL is disposed in parallel with the signal line X. However, the pixel electrode EP is aligned with the scan line Y. In the configuration having the parallel slit SL, when the second common electrode COM2 parallel to the slit SL is disposed in parallel with the scanning line Y, the peripheral edge facing the scanning line Y of the pixel electrode EP can be made effective, and the embodiment The same effect can be expected.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows roughly the structure of the liquid crystal display device of the liquid crystal mode using the transverse electric field which concerns on one Embodiment of this invention.

FIG. 2 is a cross-sectional view schematically showing the structure of an array substrate applied to the liquid crystal display shown in FIG. 1. FIG.

FIG. 3 is a plan view schematically showing the structure of one pixel of an array substrate applied to the liquid crystal display shown in FIG. 1; FIG.

4A is a plan view schematically showing the structure of a pixel of an array substrate in this embodiment;

4B is a diagram schematically showing a cross-sectional structure of the array substrate when the array substrate shown in FIG. 4A is cut at line A-B.

FIG. 4C is a diagram schematically showing a cross-sectional structure of a liquid crystal display panel when the array substrate shown in FIG. 4A is cut at the line C-D. FIG.

5A is a plan view schematically showing the structure of a pixel of an array substrate in a comparative example.

FIG. 5B is a diagram schematically showing a cross-sectional structure of a liquid crystal display panel when the array substrate shown in FIG. 5A is cut at line A-B. FIG.

6A is a plan view schematically illustrating the structure of a pixel of an array substrate in a modification of the present embodiment.

FIG. 6B is a diagram schematically showing a cross-sectional structure of the array substrate when the array substrate shown in FIG. 6A is cut at line A-B. FIG.

<Explanation of symbols for the main parts of the drawings>

20, 30: insulated substrate

32: black matrix

34: color filter layer

36a, 36b: alignment film

XD: Signal Line Driver

CNT: Controller

YD: Scan Line Driver

Claims (5)

A liquid crystal display device having a structure in which a liquid crystal layer is held between a pair of substrates, A scanning line extending in the row direction of the pixel, A signal line extending in the column direction of the pixel, A pixel electrode disposed for each pixel and having a slit; A first common electrode facing the pixel electrode via an interlayer insulating film; A second common electrode extending in parallel with the slit and disposed adjacent to the pixel electrode in the same layer as the pixel electrode; The liquid crystal display device characterized by the above-mentioned. The method of claim 1, The said slit is formed in parallel with a column direction, The liquid crystal display device characterized by the above-mentioned. The method of claim 1, And the pixel electrode and the second common electrode are formed of the same conductive material. The method of claim 1, And the second common electrode is opposed to the signal line via an insulating film. The method of claim 4, wherein And the second common electrode has an opening facing the signal line.

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